Are You Eating Too Much Protein For Your Age?

The claim: Lean protein is a weight loss wonder because it stokes your metabolism and helps you stay fuller longer. But eating a diet that’s high in protein is associated with a heightened risk for cancer and mortality, finds new research published in the journal Cell Metabolism.

The research: Researchers at the University of California, Los Angeles tracked 6,381 adults ages 50 and older for 18 years using data from the National Health and Nutrition Examination Survey. Depending on their protein consumption, subjects were placed in high protein (more than 20% of calories from protein), moderate protein (11% to 19%), or low protein (10% or less) categories. Adults under age 65 who ate a high-protein diet were four times more likely to die from cancer or diabetes and twice as likely to die from other causes. Those who ate a moderate-protein diet were three times as likely to die from cancer. However, the effects were reversed for older participants: Adults over 65 who ate moderate to high amounts of protein were at decreased risk for dying from cancer or any other cause.

What it means: Protein may activate IG-F1, a hormone in the body responsible for cell growth. “The theory is that as you’re pushing cells to grow, you’re pushing them to age more quickly,” says study co-author Valter Longo, PhD. And when cells are pushed to divide rapidly, disease-causing DNA damage is likely to occur. “By contrast, when you have low-level growth factors, cells sit in a standby mode associated with protecting [the body], and potentially making sure that maintenance is carried out versus putting effort into dividing and growing,” he says. But for older adults who tend to be smaller and more frail, the boost in cell growth activity that comes from eating a protein-rich diet could help the immune system respond more rapidly to infection.

The bottom line: For younger adults, less protein might be better than more, Dr. Longo says. He suggests following the minimum guidelines set by the American Institute of Medicine of 0.8 grams of protein per kilogram of weight (about 58 grams for a 160-pound adult). And stick to mostly plant proteins, whose amino acids differ from animal-based proteins and may have a different effect on the body’s aging activity. Over 65? Talk to your doctor about eating a higher-protein diet, Dr. Longo says.